They co-star in the Avengers movies together but clearly Robert Downey Jr and Jeremy Renner are close pals off set too.

The duo - who play Iron Man/Tony Stark and Hawkeye respectively in the Marvel franchise -spent the weekend together in Nashville with their families where they were spotted at a music festival and enjoying lunch at Urban Grub on Saturday and at the zoo on Monday.

Robert, 49, was accompanied by his wife Susan and their two-year-old son Exton while Jeremy, 43, brought daughter Ava, 15 months and ex-girlfriend Sonni Pacheco along with him.

Daddy duty: Robert Downey Jr and Jeremy Renner spent time together in Nashville over the weekend with their families

The duo attended the Sevier Park Festival, which is co-sponsored by Nashville Underground Radio on Saturday before grabbing some lunch at Urban Grub.

A source told E! News: 'It was Saturday around 4 pm Robert Downey Jr. was hanging out at the festival.

Daddy's boy: Robert carried two-year-old son Exton in his arms as they left a restaurant following brunch over the weekend

'Zeke Duhon was performing on stage. Downey was in the crowd. He was just hanging around and listening to the music.

'He was with Jeremy Renner. They seemed to be having a good time.'

Cosy: Jeremy looked thrilled to have his daughter and her mother with him as he soaked up the sun at Nashville zoo

And Urban Grub's general manager Garth Nash told the website: 'It was Saturday around 2 pm and they stayed until about 3:30 to 4 pm.

'Robert Downey Jr. and Jeremy Renner and several others came in and ordered off the brunch menu.

Matching: Exton and his dad wore matching orange caps while Sonni cradled baby Ava in her arms during the excursion

'They sat out in the beer garden patio. It was a beautiful day. They seemed to enjoy themselves and were having a great time.'

However, by Sunday it was family time and the co-stars brought their families to Mike's Ice Cream and Coffee for a treat.

Taking a break: After recently filming scenes for the Avengers sequel in London, it's not surprising Renner was eager to take a break

While they were relaxed and down to earth, two bodyguards were present the entire time, revealing that this was no ordinary family day out.

An insider told E! News: 'It was Sunday afternoon about 4:30 pm and they stayed about a half hour.

Back on? While Jeremy and Sonni Pacheco split before daughter Ava was born, the former couple spent the weekend together in Nashville

'Robert Downey Jr. was with his family and Jeremy Renner [with his].

'It looked like the ladies were sitting together and the kids were sitting together and Robert and Jeremy were talking. It looked like a couple of families going out together.

Under control: Robert maintained a low profile in his sweatpants and baseball cap as he carried his son's bottle for him

'Robert got a triple shot of espresso and they rest of the group got shakes and ice cream. They had two bodyguards with them.

'They seemed like a regular family that came in for ice cream and coffee on a Sunday afternoon. It looked like a normal family outing. They didn't make a spectacle and several people didn't even realize that he [Robert Downey Jr.] was there.'

Low key: The group managed to maintain a low profile as they took in the sights of Nashville on a break from filming

On Monday the two families spent the day at Nashville zoo and although Jeremy and Sonni split before Ava's birth, they looked every inch a couple as they doted on their daughter.

Both men were casual with Renner in jeans, Downey Jr in sweatpants and both in T-shirts and baseball caps while the women also dressed down.

Recently Robert and Jeremy were filming the Avengers sequel in London with co-stars including Chris Hemsworth, Scarlett Johansson and Mark Ruffalo.

Protected: The group brought a couple of bodyguards with them on their family vacation